MULTIWAVELENGTH FLARE OBSERVATIONS - TEMPORAL EVOLUTION OF THE 20 AUGUST 1992 FLARE

The 20 August 1992 flare around 14:28 UT was observed in H alpha, H ep silon and Ca II H with the imaging spectrographs at Locarno-Monti, Swi tzerland, with the radiotelescopes in Bern, and in soft and hard X-ray s by the Yohkoh satellite. In this paper we discuss the analysis of th e temporal and spatial evolution of this flare, well observed at chrom ospheric and coronal layers. We find that the chromospheric electron d ensity shows well-correlated rises with the hard X-rays emphasizing th e direct response of the chromosphere to the energy deposition. Althou gh both footpoints of the loops show simultaneous rises of the electro n density, non-thermal electron injection is only observed in one of t he footpoints, while an additional heating mechanism, like thermal con duction, must be assumed for the other footpoint. However, it is puzzl ing that all the chromospheric observations in both footpoints are del ayed by approximate to 3 s compared to the hard X-ray light curve. Alt hough this would be compatible with the thermal heating of one footpoi nt, it is in contradiction to the non-thermal heating of the other one . Finally, we observed evidence that during the first part of the flar e a thermal conduction front propagates at a speed of approximate to 2 000 km s(-1) into a second loop, in which the energy release occurs in the second part of the flare.